physical contact? karaoke? the outdoors? What does that have to do with rationality? Genuine progress requires Weirdtopia, not just Eutopia.
Physical contact and the outdoors, at least, pattern-match to me as something that a) are inherently enjoyable to the typical human brain, and b) that the stereotypical LessWrong member, a somewhat geeky male, doesn't already do a lot of. Low-hanging fruit, I guess–although I should beware of stereotypes and pattern-matching, because I'm probably mostly wrong.
I understand that you're trying to build a community... I just have no idea why.
Because being part of a community is something that, for most people, is just innately nice...and being in a community of people with particular values and habits makes most people better at living up to those values and building those habits.
One of the nice things about a community is being able to talk to a bunch of people who, although you may not know them personally, are not far from you in inferential distance and share much of the same jargon/vocabulary. Less Wrong has a very particular jargon, which isn't shared by other "skeptics" meetups, and the focus of discussion is slightly different: thinking accurately, making good decisions, and achieving goals, along with a bunch of Singularity memes...there is some overlap with other skeptics' meetups, but not totally.
There are already a ton of communities organized around religion, and it's been tempting for me in the past to go to church just because it provided a ready-made community of nice people who were already in the habit of being helpful to each other, singing together, etc. I don't know if the instinct to latch onto a community is stronger or weaker in myself than in the average LWer, but it would certainly be nice to have a possible community of people who actually shared my beliefs.
This is an extremely important question, and I think Swimmer's answer, while true, is not sufficient. Having additional goals beyond just forming a community will probably make people more attracted/committed to the group. Simply working together towards a common goal brings people closer together.
One thing I would like to mention is that you have a great chance to experiment with group design. I would strongly suggest setting goals/predictions in advance, taking detailed notes on your progress, and generally using this as a chance to collect data that LW groups in the future can use.